Comparison of anomalous Doppler resonance effects with molybdenum and graphite limiters on HT-7

Wang, Y. M.; Gao, Xiang; Ling, Bili; Liu, Y.; Zhang, S. B.; Han, Xingwei; Ti, Ang; Li, E. Z.

doi:10.1063/1.3695093

Cited by 5 publications

(3 citation statements)

References 17 publications

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“…Several previous studies of the pedestal collapse have reported the abrupt increase of the mm-wave emission intensity, whose frequencies correspond to the ECE harmonics at the edge region [42][43][44][45][46][47]. The details of the generation mechanism in the mm-wave bursts are still controversial.…”

Section: Discussionmentioning

confidence: 99%

Intense whistler-frequency emissions at the pedestal collapse in KSTAR H-mode plasmas

Kim¹,

Thatipamula²,

Kim³

et al. 2020

Nucl. Fusion

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The edge confinement barrier of high-confinement mode (H-mode) plasma involves a variety of plasma waves alongside with fluid instabilities and collective particle transport during the barrier collapse. We demonstrate a new method of resolving the plasma waves by measuring the modulations embedded in the second harmonic electron cyclotron emission (ECE). Utilizing mm-wave heterodyne detection and fast digitization technologies on the KSTAR tokamak, we resolve not only the frequency spectrum but the wavenumber as well. At the plasma boundary during the barrier collapse, we observe multiple bursts of broadband whistler-frequency (<8 GHz) waves, together with intense narrowband emissions. The narrowband emissions exhibit rapid rising and falling tones within a few microseconds. Bispectral analyses reveal the existence of nonlinear interactions between the broadband and the narrowband waves, confirming their concurrence in the barrier zone. We estimate that the vertical wavenumber of the narrowband waves is comparable to that of a whistler wave, utilizing multiple mm-wave mixer channels. Our work opens a new experimental way to study wave–wave and wave–particle interactions in magnetically confined plasmas.

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Section: Discussionmentioning

confidence: 99%

Intense whistler-frequency emissions at the pedestal collapse in KSTAR H-mode plasmas

Kim¹,

Thatipamula²,

Kim³

et al. 2020

Nucl. Fusion

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“…In this Letter we show for the first time that BMEs in MAST can be attributed to the presence of suprathermal, magnetic-field-aligned electron populations that drive waves in the EC range via the anomalous Doppler instability (ADI). This instability has been observed recently on the HT-7 tokamak [15] and is also believed to play a role in the dynamics of energetic electrons in solar flares [16,17] and the excitation of whistlers in the solar wind [18]. The production and evolution of energetic electron popu lations continue to be of topical interest in the solar context [19].…”

mentioning

confidence: 82%

Electron Kinetics Inferred from Observations of Microwave Bursts During Edge Localized Modes in the Mega-Amp Spherical Tokamak

et al. 2015

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Recent measurements of microwave and x-ray emission during edge localized mode (ELM) activity in tokamak plasmas provide a fresh perspective on ELM physics. It is evident that electron kinetics, which are not incorporated in standard (fluid) models for the instability that drives ELMs, play a key role in the new observations. These effects should be included in future models for ELMs and the ELM cycle. The observed radiative effects paradoxically imply acceleration of electrons parallel to the magnetic field combined with rapid acquisition of perpendicular momentum. It is shown that this paradox can be resolved by the action of the anomalous Doppler instability which enables fast collective radiative relaxation, in the perpendicular direction, of electrons accelerated in the parallel direction by inductive electric fields generated by the initial ELM instability.

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“…It has been found in over four decades of experiments in low density tokamak plasmas [4][5][6][7][8]11,14 with both Ohmic and lower hybrid current drive, and remains topical. For example, the ADI is believed to explain the recently observed relaxation oscillations in directional hard X-ray signals emitted by the energetic electron population in the HT-7 tokamak 14,15 . These observations reflect the underlying physics of the ADI, which involves a shift of energy from parallel to perpendicular particle motion, accompanied by the excitation of waves at frequency and wavenumber (ω, k) satisfying the anomalous Doppler resonance condition 11 ,…”

Section: The Anomalous Doppler Instability (Adi)mentioning

confidence: 99%

Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas

2013

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Suprathermal tails in the distributions of electron velocities parallel to the magnetic field are found in many areas of plasma physics, from magnetic confinement fusion to solar system plasmas. Parallel electron kinetic energy can be transferred into plasma waves and perpendicular gyration energy of particles through the anomalous Doppler instability (ADI), provided that energetic electrons with parallel velocities v ≥ (ω + Ω ce )/k are present; here Ω ce denotes electron cyclotron frequency, ω the wave angular frequency and k the component of wavenumber parallel to the magnetic field. This phenomenon is widely observed in tokamak plasmas. Here we present the first fully self-consistent relativistic particle-in-cell simulations of the ADI, spanning the linear and nonlinear regimes of the ADI. We test the robustness of the analytical theory in the linear regime and follow the ADI through to the steady state. By directly evaluating the parallel and perpendicular dynamical contributions to j · E in the simulations, we follow the energy transfer between the excited waves and the bulk and tail electron populations for the first time. We find that the ratio Ω ce /(ω pe + Ω ce ) of energy transfer between parallel and perpendicular, obtained from linear analysis, does not apply when damping is fully included, when we find it to be ω pe /(ω pe + Ω ce ); here ω pe denotes the electron plasma frequency. We also find that the ADI can arise beyond the previously expected range of plasma parameters, in particular when Ω ce > ω pe . The simulations also exhibit a spectral feature which may correspond to observations of suprathermal narrowband emission at ω pe detected from low density tokamak plasmas.

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Comparison of anomalous Doppler resonance effects with molybdenum and graphite limiters on HT-7

Cited by 5 publications

References 17 publications

Intense whistler-frequency emissions at the pedestal collapse in KSTAR H-mode plasmas

Intense whistler-frequency emissions at the pedestal collapse in KSTAR H-mode plasmas

Electron Kinetics Inferred from Observations of Microwave Bursts During Edge Localized Modes in the Mega-Amp Spherical Tokamak

Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas

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